The present invention relates to a gun barrel capable of achieving satisfactory life when firing high-energy ammunition and, more particularly, to a novel multi-layer composite gun barrel having a co-extruded composite multi-layered fore portion and a lined multi-layered breech portion.
Gun barrels are highly stressed by a combination of pressures up to 100,000 psi and very severe cycles resulting from temperature changes of several million .degree.F per second. Current forms of gun barrels have relatively low lives. As larger quantities of high flame temperature propellant are used to achieve higher ammunition performance, the demand on the barrels becomes much greater, particularly for multiple rounds fired in a short time interval. The demand on the gun barrel during long bursts can be broken down into two distinct regions--the bore surface and the outer jacket. The bore surface experiences extreme variations in temperature which causes almost immediate cracking and the beginning of low cycle fatigue failures. High energy ammunition and high flame temperature propellant greatly accelerate these problems. High temperatures also cause loss of protective chrome plate, melting, and subjects the bore to hot gas erosion. Under these conditions, the barrel must still resist stresses created during engraving of the rotating band, projectiles which are launched into the barrel and high velocity projectile contact with the barrel. In conventional projectiles which are spun up in the barrel, the bore must withstand the stresses from a spinning projectile, which can result in sever balloting and body engraving in hot thermally expanded bores. The bore must still be able to withstand attack by chemical compounds after having been left under high tensile stresses due to compressive yielding during firing. This stress corrosion frequently causes propagation of deep cracks.
The outer portion of the barrel, on the other hand, has a relatively kinder environment with less rapid changes in temperature and stresses. However, the outer portion of the barrel must withstand the high pressure transmitted through the severely degraded bore surface, and must maintain a high modulus of elasticity to maintain low bore expansion and axial stiffness during firing. The barrel outer, or jacket, portion must have good cleanliness and fracture toughness to prevent rapid crack growth after propagation from the bore surface, which can lead to rupture. Unfortunately, these characteristics must be achieved over a significant temperature range, which will cause yielding during most firing bursts. The coefficient of thermal expansion of the jacket becomes particularly important in limiting bore growth when the barrel jacket gets hot.
The obvious solution to the extremely different conditions of the bore surface and the jacket portion is to utilize a composite barrel with optimum properties for each region. Many concepts have been advanced for achieving the desired configuration, including concepts which provide a good bond between the boreliner and the jacket. However, none of these designs has provided a good low cost method of achieving acceptable erosion rates in the breech end of the barrel and good concentricity between the liner and jacket in the bonded forward section, or fore portion, of the barrel. Good concentricity is required to prevent barrel bending due to differential expansion. It is therefore highly desirable to provide a relatively low cost multi-layer composite gun barrel with acceptable breech end erosion and concentricity attributes.